1. Field of the Invention
The present invention relates generally to the field of mobile communications, and more specifically to estimating the position of a mobile station using network information.
2. Relevant Background
Wireless devices, such as mobile stations (MSs) or terminals, are widely used for various purposes. One key use of wireless devices is for communication with a wireless communication network for voice, packet data, and the like. Another emerging use of these wireless devices is for position determination, which may be desirable or necessary in certain circumstances. For example, the Federal Communications Commission (FCC) has adopted a report and order for an enhanced 911 (E-911) wireless service that requires the location of a wireless device (for example, a cellular phone) to be provided to a Public Safety Answering Point (PSAP) each time a 9-1-1 call is made from the device. The FCC mandate requires the location of the wireless device to be accurate to within 50 meters for 67% of calls and within 150 meters for 95% of calls.
In addition to the FCC mandate, service providers have begun to recognize that location services (that is, services that identify the position of a wireless device) may be used in various applications to provide value-added features that may generate additional revenue for the service providers. For example, a service provider may use location services to implement location-sensitive billing such that different rates may be charged for calls originating from different zones. A service provider may also use location services to provide location-sensitive information such as driving directions, local information on traffic, gas stations, restaurants, hotels, and the like. Other applications that may be provided using location services include asset tracking services, asset monitoring and recovery services, fleet and resource management, personal-location services, gaming, and personal security, among others.
Wireless communication networks are in the process of offering increasingly sophisticated capabilities for determining the position of a wireless device within the network. In a code division multiple access (CDMA) digital cellular network, for example, the position determination capability can be provided by advanced forward link trilateration (AFLT), a technique that computes the location of the wireless device from the measured time of arrival of radio signals transmitted from earth bound base stations. A more advanced technique is hybrid position determination, where the wireless device employs a Global Positioning System (GPS) receiver and the position is computed based on both AFLT and GPS measurements.
There are a number of known message protocols and formats for CDMA position determination employing AFLT, GPS, and hybrid receivers. Existing position determination technologies have achieved considerable success by providing location measurements rapidly and with precision.